Method for drying encapsulated motor compressors for refrigerating units



G. JOHANSSON O 3,521,372

METHOD FOR DRYING ENCAPSULATED MOTOR COMPRESSORS FOR REFRIGERATING Original Filed Oct. 25, 1967 SUCTION OUTLET lll I GASKEIQT VACUUM AIR PUMP \PERCHLOROETHYLENE COOLING HEATING United States Patent 3 521,372 METHOD FOR DRYING ENCAPSULATED MOTOR COMPRESSORS FOR REFRIGERATING UNITS Gustav Johansson, Nordborg, Denmark, assignor to Danfoss A/S, Nordborg, Denmark, a company of Denmark Continuation of application Ser. No. 677,421, Oct. 23, 1967. This application May 5, 1969, Ser. No. 824,362 Int. Cl. F26b 5/04, 7/00 US. Cl. 34-15 6 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a method of drying or dehydrating the internal cavity regions of encapsulated or sealed motor-compressor units of the type used for refrigerators. The method involves two main stages. In the first stage the motor-compressor units are placed in an enclosure containing a vaporous drying agent at a temperature which is higher than the boiling point of water. The moisture in the internal cavity regions of the motorcompressor units vaporizes and is substantially displaced by the vaporous drying agent. In the second stage the internal cavityregions are'placed in fluid communication with a suction pump which draws the vaporous drying agent out of the cavities without any additional heat being supplied.

This invention relates to a method for drying encapsulated motor compressors for refrigerating units whereby, in a first stage, moisture is eliminated by means of a vaporous drying agent, for example, pre-ethylene chloride, which condenses on the compressor components and, in a second stage, the drying agent is removed;

A process of this type is known in which the motor compressor, in a first stage, is brought into contact with per-ethylene chloride vapour of a temperature of 119 C., which latter immediately condenses On all parts of the motor compressor. In this way the whole motor compressor is rapidly raised to a temperature above the boiling point of water, so that all the water contained in the motor compressor evaporates. The per-ethylene chloride, moreover, penetrates into all cavities and removes the water vapor from them. The unit is then transferred into a second chamber charged with hot air or hot nitrogen. The hot air serves to heat the motor compressor components to about 150 C., so that the condensed per-ethylene chloride evaporates again and is completely driven out by being replaced by air or nitrogen. Therefore, the gas in the space of the second stage has to be kept at a higher temperature and must be continuously heated. Nevertheless, it takes to minutes before the motor compressors have been raised to the desired temperature and the per-ethylene chloride has been driven out. Furthermore, certain hazards exist in the case of operational failure, for example, when a conveyor belt is used and no safety precautions have been adopted.

Whereas the two-stage drying method just described may be terminated after 45 to 60 minutes, all other known drying processes take 6 to 12 hours. Among the latter processes there is one whereby the moisture is to be eliminated by evacuation. To this purpose the motor compressor is brought into a heatable vacuum chamber while contained in its housing which latter is closed except for the connection ports. However, the drying effect is inconsiderable because the oven heat, due to the resilient suspension of the motor compressor in its housing, penetrates only slowly into the interior of the motor. In order to accelerate heating of the interior, the windings of 3,521,372 Patented July 21, 1970 ice the motor were electrically heated and/or hot air or Freon gas was introduced temporarily at normal pressure. A similarly prolonged drying time is required for another process whereby, first, dry hot air or nitrogen is introduced in the motor compressor, or circulated therein, in an oven before this drying agent is eventually sucked out. Also in these cases the hazard exists that the motor compressors are exposed to an excessively high oven temperature and damaged upon conveyor belt failure.

A main object of the invention is to provide a new and improved method for drying the interior and the interior components of a refrigeration type motor compressor unit which can be performed in considerably less time than all known methods and in the case of which the motor compressors cannot be damaged by heat when an operational failure occurs.

Other objects are achieved by using the method referred to at the beginning for the drying of encapsulated motor compressors for refrigerating units and by modifying this method in that the drying agent in the second stage is sucked off by evacuation, without the additional supply of heat.

FIG. 1 is a schematic drawing illustrating the first stage of the method of the present invention in which encapsulated motor compressor units are shown being conveyed through an oven containing a boiling vaporous drying agent; and

FIG. 2 is a schematic drawing illustrating the second stage of the method in which encapsulated motor compressor units are shown having remaining portions of the vaporous drying agent suctionally removed from the interiors of the units by a vacuum pump.

Surprisingly, the time during which the motor compressor stays in the second stage can be reduced to 2 to 6 minutes in this process, so that the overall drying time amounts to less than half an hour. In the first stage the maximum temperature is predetermined by the evaporation temperature of the drying agent. It can easily be chosen such that it is above the boiling temperature of water but below a temperature which would damage the motor compressor. A suitable temperature is the saturated vapor temperature of per-ethylene chloride, namely 119 C. Since no further supply of heat is required in the second stage, damage due to temperature is also excluded here. 1

Whereas, before now, a further supply of heat was considered necessary in order to remove the condensed drying agent, it is possible, according to the present invention, to operate without such additional supply of heat because, during evacuation, not only is the drying agent sucked off, but, due to a pressure drop, the boiling point of the drying agent is lowered at the same time, so that the sensible heat of the motor compressor, which corresponds to the condensation temperature of the drying agent at normal pressure, is entirely adequate for the evaporation of the condensed drying agent.

During the second stage the housing is preferably open. This is an advantage because then the second stage can be directly connected, without temperature drop, to the first stage in which the housing is preferably also open. A further advantage is that the suction pressure of the pump can operate on the motor compressor without substantial loss of pressure.

In a preferred embodiment of the invention the housing is placed, with the open side down, on the rubber gasket of a suction port upon which it rests by its own height. This weight, in conjunction. with the suction pressure, is fully adequate to guarantee a tight connection without screwing or some other form of locking. Such a connecting operation can also be performed fully automatically in a production line.

A rotary piston engine (Roots pump) is particularly suitable as a suction means in this case. Such an engine, While attaining the desired vacuum, has a high delivery characteristic, so that the process can be terminated within a minimum of time. An embodiment of the process of the invention will now be described in further detail.

A conveyor belt carries motor compressors into an oven, with the open end of their housings pointing down, the said oven being traversed within about 10 to 20 minutes. Liquid per-ethylene chloride is kept boiling at the bottom of the oven. The oven walls are cooled, so that the vapors circulate. The per-ethylene chloride vapor is at a temperature of 119 C. and immediately condenses on all parts of the motor compressors to be dried, until the latter have been heated within about 5 minutes to approximately the same temperature. The condensed perethylene chloride drips from the units and carries some dissolved oil and grease with it. Moreover, the per-ethylene chloride displaces the water vapor, which may have formed, from all cavities of the unit, so that, at the end of the first stage, there is a charge containing predominantly per-ethylene chloride condensate and vapor, with only a small percentage of water vapor.

Subsequently the motor compressors are removed from the oven and placed on the rubber gasket of a suction port, with the open side of their housing pointing down, the said suction port being connected to a vacuum pump in the form of a Roots pump. One vacuum pump may also be connected with several suction ports. These suction ports are preferably arranged on a revolving unit connected to the pump. The per-ethylene chloride is sucked oif through the large aperture. Due to the vacuum produced thereby, also the condensed per-ethylene chloride evaporates and is likewise sucked 01f.

When using a pump having a capacity of 150 l./s., a pressure of 0.1 mm. Hg was achieved for a compressor within two minutes, and the per-ethylene chloride content was 0.25 ml. In order to achieve the same low perethylene chloride content in the second stage by means of hot air, a time of nearly 60 minutes is required.

Then the motor compressors were removed from the suction port; the housing was closed by welding in dry air at atmospheric pressure, and was sealed airtight up to being charged with the coolant.

Other drying agents are also suitable for the process described here, especially agents whose condensation or boiling points are above the boiling point of water but below a temperature detrimental to the motor compressor.

What is claimed is:

1. A method of drying the interior and the interior components of an encapsulated refrigeration type motor compressor unit comprising the steps of starting with a unit of said type having an in-process opening in the outer housing thereof, placing said unit with said opening facing downwardly in an oven in which a supply of a vaporous drying agent having a higher boiling point than water is boiling and filling the space enclosed by the oven with the drying agent vapor, keeping said unit in said oven until said unit is heated to a temperature higher than the boiling point of water and sufiicient to impart a minimum predetermined latent heat to said unit, connecting said opening to a vacuum pump and operating the pump to suctionally withdraw remaining portions of said agent while preventing the temperature of said unit from dropping below the atmospheric condensation temperature of said agent, said pump being operated with a suctional pressure related to said minimum predetermined latent heat to eifect the substantially complete withdrawal of said agent, and disconnecting said unit from said vacuum pump and hermetically sealing said housing by closing said opening in a dry atmosphere as by welding.

2. A method according to claim 1 wherein said drying agent is per-ethylene chloride.

3. A method according to claim 1 wherein said drying agent is perchloroethylene.

4. A method according to claim 1 wherein said unit is removed from said oven prior to said step of suctionally withdrawing remaining portions of said agent.

5. A method according to claim 1 wherein said unit is maintained in proximity to said boilng agent for a period of approximately 10 to 20 minutes and step of suctionally withdrawing remaining portions of said agent is performed for a period of approximately 2 to 6 minutes.

6. A method according to claim 1 wherein the temperature of said unit is maintained above the atmospheric condensation temperature of said agent without supplying additional heat during the step of suctionally withdrawing remaining portions of said agent.

FREDERICK L. MATTESON, JR., Primary Examiner H. B. RAMEY, Assistant Examiner US. Cl. X.R. 34-21 

